In the testing of electrical components, wherein a plurality of components in an electrical circuit are to be tested, it has been difficult to identify failed components in situ, while the components remain in the circuit, because of the difficulty of distinguishing electrical characteristics of a respective component from those of associated components or groups of components within the circuit. Additionally, it has been difficult to test individual components sequentially in circuits having large numbers of such components. This invention is particularly applicable for testing components in situ, particularly those which fail in an open or nonconductive condition, wherein current is not permitted to pass readily through the components. For example, in illuminated display systems, such as displays incorporating arrays of incandescent lamps, LEDs, or the like, a large number of individually illuminated devices must be maintained and serviced. Thus, in an LED array utilized in a commercial display sign, there may be as many as 10,000 or more light emitting diodes, each of which is subject to fail in an open condition. As will be apparent to those in the art, sequential testing of the resistance of each device(s) in such an array by means of individual testing procedures may be difficult and time consuming.
Accordingly, certain prior-art systems have utilized various complex testing circuits capable of evaluating the response of a plurality of such components. The testing of such arrays of electrical devices is of particular commercial interest with respect to the testing of commercial displays, which are commonly used as illuminated signs in small businesses and the like. Typically, individual LEDs in such arrays tend to fail during extended use. Whereas one or two failures will not significantly affect the appearance of the display, the appearance and legibility of the sign deteriorates as additional LEDs are burned out over time. Whereas such displays may be visually inspected for such failed devices, it is advantageous that an automated, electrical testing circuit be provided to provide timely notification to an operator that one or more LEDs have failed and for identifying the row and column of the failed device.